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PubMed2001

Topography of orientation centre connections in the primary visual cortex of the cat.

The functional topography of lateral connections to orientation-centre zones was studied by optical imaging of intrinsic signals in combination with tracer injections (fluorescent beads and biocytin) and electrophysiological recordings. Three-dimensional reconstruction of anterogradely labelled axon terminals and retrogradely labelled somata revealed a uniform distribution across all orientations in a non-patchy manner. The overall lateral extent of the labelling was 3-4 mm in layer 3, that is about half of the extent observed for orientation domain connections in the same layer. These bulk injection data are in contrast with the reportedly sharp orientation tuning of neurons of centre zones and suggest that orientation specificity here does not require highly specific connections. Nonetheless, another plausible scenario is that orientation centre connections are orientation specific but their specificity present at the single cell level cannot be revealed by bulk labelling due to their large spatial overlap.

Animals↗
PubMed1996

Visual field defects in Alzheimer's disease patients may reflect differential pathology in the primary visual cortex.

The aim of this study was to test the hypothesis that differences in density of senile plaques (SP) and neurofibrillary tangles (NFT) in the cuneal and lingual gyri of area V1 of the visual cortex could explain the predominantly inferior visual field defects seen in patients with Alzheimer's disease (AD). The density of SP and NFT was measured in the cuneal and lingual gyri of 18 AD patients. In 7/18 (39%) patients, the density of SP and/or NFT was significantly greater in the cuneal compared with the lingual gyri. In 3/18 (17%) patients, densities were greater in the lingual than the cuneal gyri and in 8/18 (44%) patients there were no significant differences among gyri. The data suggest that pathological differences between cuneal and lingual gyri could contribute to the reported visual field defects in some AD patients.

Aged↗
PubMed1998

Independent component filters of natural images compared with simple cells in primary visual cortex.

Properties of the receptive fields of simple cells in macaque cortex were compared with properties of independent component filters generated by independent component analysis (ICA) on a large set of natural images. Histograms of spatial frequency bandwidth, orientation tuning bandwidth, aspect ratio and length of the receptive fields match well. This indicates that simple cells are well tuned to the expected statistics of natural stimuli. There is no match, however, in calculated and measured distributions for the peak of the spatial frequency response: the filters produced by ICA do not vary their spatial scale as much as simple cells do, but are fixed to scales close to the finest ones allowed by the sampling lattice. Possible ways to resolve this discrepancy are discussed.

Animals↗
PubMed1985

Development of cortical afferents and cortico-tectal efferents of the mammalian (rat) primary visual cortex.

At the time when the fibres from the striate cortex (area 17) begin to innervate the superficial layers of the superior colliculus of the young rat (postnatal days 4 and 5) a high degree of specificity in the organization of this newly formed cortico-tectal projection is already apparent. Thus, in young rats, as in adult mammals of virtually all species studied so far, the somata of cortico-tectal neurones are confined to lamina V of the ipsilateral cortex. However, this high degree of laminar (radial) specificity in young animals is accompanied by a substantial degree of exuberance as indicated by a tangential distribution of the cortico-tectal cells which is wider than that in the adult. The exuberant projections are pruned during the second postnatal week. The cortico-cortical associational and commissural fibres start to enter the grey matter of the rat striate cortex after postnatal day 7. Again a high degree of specificity in the laminar distribution of those newly established projections is apparent. However, the cortico-cortical projection, at the time when cortico-cortical fibres enter the cortical laminae, is clearly exuberant since the tangential spread of cortical cells projecting to the striate cortex is wider than that in the adult. Pruning of these excessive projections takes place some time after postnatal day 14. It is believed that understanding the mechanism(s) underlying the development of connections of the rat visual cortex might be of general importance in understanding developmental abnormalities in the pattern of interconnections of the visual cortices of other mammalian orders.

Afferent Pathways↗
PubMed1997

Spatial resolution and contrast sensitivity of single neurons in area 19 of split-chiasm cats: a comparison with primary visual cortex.

Electrophysiological recordings were carried out in the callosal recipient zone of area 19 in normal and split-chiasm cats and, for comparison purposes, at the border of areas 17 and 18 of split-chiasm cats. The influences of retinothalamic and callosal inputs on a single cortical neurons were thereby evaluated. Extracellular recordings of single cells were made in anaesthetized and paralysed cats in the zone representing the central visual field. Receptive field properties were assessed using sine wave gratings drifting in optimal directions. Results showed that in area 19 and areas 17/18 one-third of the cells were binocularly driven after section of the optic chiasm. In area 19, the spatial resolution and contrast sensitivity of cells driven via the dominant eye were similar in the normal and split-chiasm groups. In areas 17/18 and area 19 of split-chiasm cats, binocular cells showed significant interocular matching of their receptive field properties (spatial resolution and contrast threshold), although small differences were observed. These small interocular differences were related to the cell's ocular dominance rather than to the signal transmission route (thalamic or callosal).

Animals↗
PubMed1997

The perceptual grouping criterion of colinearity is reflected by anisotropies of connections in the primary visual cortex.

An important step in the processing of visual patterns is the segmentation of the retinal image. Neuronal responses evoked by the contours of individual objects need to be identified and associated for further joint processing. These grouping operations are based on a number of Gestalt criteria. Here we report that connections in the visual cortex of the cat exhibit a highly significant anisotropy, preferentially linking neurons activated by contours that have similar orientation and are aligned colinearly. These anatomical data suggest a close relation between the perceptual grouping criterion of colinearity and the topology of tangential intracortical connections. We propose that tangential intracortical connections support perceptual grouping by modulating the saliency of distributed cortical responses in a context-dependent way. The present data are compatible with the hypothesis that the criteria for this grouping operation are determined by the architecture of the tangential connections.

Animals↗
PubMed1997

Actions of compounds manipulating the nitric oxide system in the cat primary visual cortex.

1. We iontophoretically applied NG-nitro-L-arginine (L-NOArg), an inhibitor of nitric oxide synthase (NOS), to cells (n = 77) in area 17 of anaesthetized and paralysed cats while recording single-unit activity extracellularly. In twenty-nine out of seventy-seven cells (38%), compounds altering NO levels affected visual responses. 2. In twenty-five out of twenty-nine cells, L-NOArg non-selectively reduced visually elicited responses and spontaneous activity. These effects were reversed by co-application of L-arginine (L-Arg), which was without effect when applied alone. Application of the NO donor diethylamine-nitric oxide (DEA-NO) produced excitation in three out of eleven cells, all three cells showing suppression by L-NOArg. In ten cells the effect of the soluble analogue of cGMP, 8-bromo-cGMP, was tested. In three of those in which L-NOArg application reduced firing, 8-bromo-cGMP had an excitatory effect. In six out of fifteen cells tested, L-NOArg non-selectively reduced responses to NMDA and alpha-amino-3-hydroxy-5-methylisoxasole-4-propionic acid (AMPA). Again, co-application of L-Arg reversed this effect, without enhancing activity beyond control values. 3. In a further subpopulation of ten cells, L-NOArg decreased responses to ACh in five. 4. In four out of twenty-nine cells L-NOArg produced the opposite effect and increased visual responses. This was reversed by co-application of L-Arg. Some cells were also affected by 8-bromo-cGMP and DEA-NO in ways opposite to those described above. It is possible that the variety of effects seen here could also reflect trans-synaptic activation, or changes in local circuit activity. However, the most parsimonious explanation for our data is that NO differentially affects the activity of two populations of cortical cells, in the main causing a non-specific excitation.

Acetylcholine↗
PubMed1977

Laminar differences in receptive field properties of cells in cat primary visual cortex.

1. Cells in area 17 of the cat visual cortex were studied with a view towards correlating receptive field properties with layering. A number of receptive field parameters were measured for all units, and nearly every unit was marked with a microlesion to determine accurately the layer in which it was found.2. Cells were defined as simple or complex by mapping with stationary stimuli, using the criteria of Hubel & Wiesel (1962). Complex cells fell into two groups: those that showed summation for increased slit length (standard complex) and those that did not (special complex).3. The simple cells were located in the deep part of layer 3, in layer 4, and in layer 6. This corresponds to the distribution of afferents from the dorsal layers of the lateral geniculate nucleus. In these cortical layers the simple cells differed primarily with respect to their receptive field size, cells in layer 4 having the smallest, layer 3 intermediate, and layer 6 the largest fields. Layer 4 was the only layer in which simple cells showed end-inhibition (a reduction in response to slits extending beyond the excitatory portion of the receptive field).4. The standard complex cells were found in all layers, but were quite scarce in layer 4. As with the simple cells, field size varied with layer: in layer 2+3 they had small to intermediate field sizes, in layer 5 intermediate, and in layer 6 very large. Layer 6 cells showed summation for slits of increased length up to very large values, and responded best when the slits were centred in the receptive field. The only standard complex cells that showed end-inhibition were those in layer 2+3, and these were similar to the layer 4 simple cells in terms of proportion of end-inhibited units and degree of end-inhibition.5. The special complex cells, originally described by Palmer & Rosenquist (1974), were found in two tiers: the upper one at the layer 3/layer 4 border and the lower one in layer 5. They were different from the standard complex cells in having a high spontaneous activity, high velocity preference, and large fields which were similar in size (at a given eccentricity) from one cell to the next. Many showed reduced response to slits of increasing length, even for slits that did not extend beyond the borders of the responsive region.6. Cells in layer 6 (the origin of the corticogeniculate projection) were antidromically activated from the lateral geniculate nucleus. The antidromically activated units included both simple and complex cells, and they had the long receptive fields characteristic of the overall population of cells in layer 6.7. The results showed that there are different types of simple and complex cells, and that cells in different layers have different properties. Taken together with their differences in site of projection, this demonstrates that the anatomical lamination pattern is reflected in functional differences between cells in different layers.

Action Potentials↗
PubMed1986

Continuity of orientation columns between superficial and deep laminae of the cat primary visual cortex.

1. Recent reports of a marked and consistent dislocation between orientation columns in the superficial and deep layers of cat striate cortex (Bauer, 1982, 1983) directly contradict the traditional view of the system (Hubel & Wiesel, 1962). This has considerable implications for our current understanding of cortical organization, and in order to clarify the issue we have carried out experiments to test the continuity of the columnar system with depth, in central regions of area 17. 2. In twenty-four penetrations, eighteen of which were placed as perpendicular as possible to the surface of the cortex, orientation preference was assessed at regular intervals both qualitatively and using a randomly interleaved quantitative technique. The distribution of preferred orientations was analysed with reference to a detailed histological reconstruction of the electrode track, including the location of laminar boundaries and the course of radial tiers of cells and capillaries. 3. From a further series of eighteen near-perpendicular penetrations, the change in average orientation between one superficial and one deep layer recording site was compared with the deviation of the track from perpendicular to the surface and hence parallel to the orientation columns. 4. In penetrations perpendicular to the surface of the cortex, orientation preference showed little variation between superficial and deep laminae. In oblique penetrations, preferred orientation generally changed according to a single, smooth trend. Those irregularities that were encountered were confined to oblique penetrations, and were distributed throughout the cortical laminae. 5. In conclusion, our evidence does not support the presence of a systematic discontinuity with depth within the orientation columnar system. It is therefore entirely consistent with earlier evidence on the subject.

Animals↗
PubMed1981

Spatial frequency columns in primary visual cortex.

Using the activity-dependent 2-[14C]deoxy-D-glucose technique, we have demonstrated a columnar organization of spatial frequency--specific sensitivity in striate cortex. Cats viewing patterns containing a single spatial frequency presented at all orientations show columns of increased deoxyglucose uptake extending through all cortical layers. A control stimulus containing all spatial frequencies presented at all orientations produces no columnar density differences within the striate cortex.

Animals↗
PubMed1990

Temporal encoding of two-dimensional patterns by single units in primate primary visual cortex. I. Stimulus-response relations.

1. Previously we developed a new approach for investigating visual system neuronal activity in which single neurons are considered to be communication channels transmitting stimulus-dependent codes in their responses. Application of this approach to the stimulus-response relations of inferior temporal (IT) neurons showed that these carry stimulus-dependent information in the temporal modulation as well as in the strength of their responses. IT cortex is a late station in the visual processing stream. Presumably the neuronal properties arise from the properties of the inputs. However, the discovery that IT neuronal spike trains transmit information in stimulus-dependent temporally modulated codes could not be assumed to be true for those earlier stations, so the techniques used in the earlier study were applied to single-striate cortical neurons in the studies reported here. 2. Single-striate cortical neurons were recorded from three awake, fixating rhesus monkeys. The neurons were stimulated by two sets of patterns. The first set was made up of 128 black-and-white patterns based on a complete, orthogonal set of two-dimensional Walsh-Hadamard functions. These stimuli appear as combinations of black-and-white rectangles and squares, and they fully span the range of all possible black-and-white pictures that can be constructed in an 8 x 8 grid. Except for the stimulus that appeared as an all-white or all-black square, each stimulus had equal areas of white and black. The second stimulus set was made up of single bars constructed in the same 8 x 8 grid as the Walsh stimuli. These were presented both as black against a gray background and white against a gray background. The stimuli were centered on the receptive field, and each member of the stimulus set was presented once before any stimulus appeared again. 3. The responses of 21 striate cortical neurons were recorded and analyzed. Two were identified as simple cells and the other 19 as complex cells according to the criteria originally used by Hubel and Wiesel. The stimulus set elicited a wide variety of response strengths and patterns from each neuron. The responses from both the bars and the Walsh set could be used to differentiate and classify simple and complex cells. 4. The responses of both simple and complex cells showed striking stimulus-related strength and temporal modulation. For all of the complex cells there were instances where the responses to a stimulus and its contrast-reversed mate were substantially different in response strength or pattern, or both.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1990

Temporal encoding of two-dimensional patterns by single units in primate primary visual cortex. II. Information transmission.

1. Previously, we studied how picture information was processed by neurons in inferior temporal cortex. We found that responses varying in both response strength and temporal waveform carried information about briefly flashed stationary black-and-white patterns. Now, we have applied that same paradigm to the study of striate cortical neurons. 2. In this approach the responses to a set of basic black and white pictures were quantified through use of a set of basic waveforms, the principal components (extracted from all the responses of each neuron). We found that the first principal component, which corresponds to the response strength, and others, which correspond to different basic temporal activity patterns, were significantly related to the stimuli, i.e., the stimulus drove both the response strength and its temporal pattern. 3. Our previous study had shown that, when information theory was used to quantify the stimulus-response relation, inferior temporal neurons convey over twice as much information in a response code that includes temporal modulation as in a response code that includes only the response strength. This study shows that striate cortical neurons also carry twice as much information in a temporal code as in a response strength code. Thus single visual neurons at both ends of a cortical processing chain for visual pattern use a multidimensional temporal code to carry stimulus-related information. 4. These results support our multiplex-filter hypothesis, which states that single visual system neurons can be regarded as several simultaneously active parallel channels, each of which conveys independent information about the stimulus.

Analysis of Variance↗
PubMed1993

Visual resolution and sensitivity of single cells in the primary visual cortex (V1) of a nocturnal primate (bush baby): correlations with cortical layers and cytochrome oxidase patterns.

1. This study describes the response properties of V1 cortical cells in a nocturnal primate and examines the receptive field organization of these cells in relationship to anatomically defined layers and cytochrome oxidase (CO) rich blobs and CO poor interblob compartments. Visual resolution and contrast sensitivity are consistent with other physiological and behavioral measures in this species. Comparisons are made with response properties of the same zones in macaque monkey, as well as of area 17 of a distantly related species (cat) that also occupies a nocturnal niche. 2. The responses of single cells to drifting sinusoidal gratings were recorded in V1 (striate cortex) of anesthetized, paralyzed bush babies (Galago crassicaudatus). Cells tended to be grouped with respect to ocular dominance, orientation preference, and direction selectivity. There was a high proportion of monocularly driven cells as in macaque monkey. Only 6% of the cells were nonoriented. These were poorly tuned complex cells and bore no resemblance to nonoriented lateral geniculate nucleus (LGN)-like cells reported in layer IV of macaque monkeys. Unidirectional cells were most frequently encountered in cortical layers that receive input from the magnocellular layers of the LGN. 3. Cells were classified as simple (31%) or complex (69%) according to standard criteria. Simple cells were significantly more narrowly tuned than complex cells for both orientation and spatial frequency. Complex cells had significantly higher average optimal spatial frequencies and spatial frequency cutoffs than simple cells. Contrast sensitivity of simple and complex cells averaged 38 and 34, respectively. Spatial resolution and sensitivity of these cells matches behavioral measures in bush baby. The spatial and temporal resolution of bush baby cells are similar to those of cats, which is likely related to the nocturnal niche of both species. 4. Cells in supragranular (I-III) and infragranular (V, VI) layers differed significantly in their response characteristics. The cells in the supragranular layers had significantly higher contrast sensitivity than did the cells in the infragranular layers. Cells in the supragranular layers likewise had higher temporal frequency cutoffs, significantly lower optimal spatial frequencies, lower spatial frequency cutoffs, and tighter orientation tuning than did cells in the infragranular layers. 5. Properties of cells in individual layers and CO blob and interblob compartments also showed differentiation. Layer III had the narrowest orientation and spatial frequency tuning with the tightest tuning in layer IIIC (IVB).(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1994

Length and width tuning of neurons in the cat's primary visual cortex.

1. The classically defined receptive field of a visual neuron is the area of visual space over which the cell responds to visual stimuli. It is well established, however, that the discharge produced by an optimal stimulus can be modulated by the presence of additional stimuli that by themselves do not produce any response. This study examines inhibitory influences that originate from areas located outside of the classical (i.e., excitatory) receptive field. Previous work has shown that for some cells the response to a properly oriented bar of light becomes attenuated when the bar extends beyond the receptive field, a phenomenon known as end-inhibition (or length tuning). Analogously, it has been shown that increasing the number of cycles of a drifting grating stimulus may also inhibit the firing of some cells, an effect known as side-inhibition (or width tuning). Very little information is available, however, about the relationship between end- and side-inhibition. We have examined the spatial organization and tuning characteristics of these inhibitory effects by recording extracellularly from single neurons in the cat's striate cortex (Area 17). 2. For each cortical neuron, length and width tuning curves were obtained with the use of rectangular patches of drifting sinusoidal gratings that have variable length and width. Results from 82 cells show that the strengths of end- and side-inhibition tend to be correlated. Most cells that exhibit clear end-inhibition also show a similar degree of side-inhibition. For these cells, the excitatory receptive field is surrounded on all sides by inhibitory zones. Some cells exhibit only end- or side-inhibition, but not both. Data for 28 binocular cells show that length and width tuning curves for the dominant and nondominant eyes tend to be closely matched. 3. We also measured tuning characteristics of end- and side-inhibition. To obtain these data, the excitatory receptive field was stimulated with a grating patch having optimal orientation, spatial frequency, and size, whereas the end- or side-inhibitory regions were stimulated with patches of gratings that had a variable parameter (such as orientation). Results show that end- and side-inhibition tend to be strongest at the orientation and spatial frequency that yield maximal excitation. However, orientation and spatial frequency tuning curves for inhibition are considerably broader than those for excitation, suggesting that inhibition is mediated by a pool of neurons.(ABSTRACT TRUNCATED AT 400 WORDS)

Action Potentials↗
PubMed1999

Neuronal origin of the transcorneal electrically evoked response in area 17 (primary visual cortex) of cats.

We investigated how the neuronal activity of the cells in area 17 of cats evoked by transcorneal electrical stimuli is associated with the transcorneal electrically evoked response (EER). Neuronal firings were associated with the negative components of the EER, N1 (9 ms latency) and N2 (20 ms latency). Excitation of a longer latency was suppressed and periodic firings were rarely found. These findings indicate that the early negative components of the EER consist of the synaptic activities over the discharge thresholds of cortical cells, and also suggest that inhibition in the visual cortex may affect the EER.

Animals↗